Scan the ingredients list of your kids' favorite sweets, and you might spot spirulina. This vitamin-packed blue-green algae has been sold in health food stores for years, but the FDA approved it for use as a food dye. Its bright-blue color is rare in nature—and highly prized by food companies. Soon it may even show up in M&M’s: The brand is testing spirulina in their blue candy coating, after pledging to cut artificial colors by 2021. Go blue!